The increasing complexity and density of integrated circuit components on printed circuit assemblies has resulted in the common use of robotic systems for manufacturing and assembly of the same. Accordingly, various techniques have been developed for the automated mounting of electronic components to printed circuit boards (PCBs). One such technique is the "hot bar thermode" bonding technique which utilizes a placement head to position an integrated circuit having a plurality of conductive leads at a desired mounting point on a PCB. Thereafter, multiple heat activatable blades are urged into contact with the conductive leads and heated to a point where the electronic component is bonded to the circuit board by means of presoldered connections thereon.
Another technique involves using a solder paste and a reflow oven. Specifically, a powdered metal such as a tin/lead composition is mixed with a liquidous flux (activator) agent whereby the mixture becomes a solder paste. The paste is positioned at a desired mounting point on the PCB, the conductive leads of the integrated circuit are placed on the solder paste, and then the assembly is heat treated in a reflow oven. The heat treatment burns off the flux, which cleans the surfaces of the pads and component, and solidifies the bonding of the component leads to the solder and PCB.
Regardless of the technique used for component placement and PCB assembly, substantial forces may be exerted on the PCB by the automated placement head. Accordingly, assembly processing requires back side support of the circuit board (or substrate) capable of withstanding such forces. The back side support must provide good, solid support for allowing even, accurate placement of components on the top side. Good support is especially needed where fine-pitched component leads are being placed. The support, however, must also avoid damaging components on the back side of the PCB in the case where a double sided board is used. Furthermore, the support must be evenly distributed and sufficiently solid under the placement area to avoid cracking of solder joints (breaking of component leads from existing solder joints) which often occurs to previously placed components on the back side of the board during the placement of another component on the top side if support is not proper.
One apparatus and method known in the art that is used for back side support is a pin insert tooling plate whereby multiple, removably adjustable support pins are manually configured in the tooling plate so that the pins are strategically positioned to best support the back side of a PCB for component placement on the top side. In the case of a double sided PCB where components are already placed on the back side, the pins must be carefully positioned to avoid contacting and damaging the components on the back side. Although this technique provides a usable solution for supporting the back side of a PCB, it entails a cumbersome, time consuming, and often difficult process to ensure the pins are properly positioned.
Another apparatus and method for supporting the back side of a PCB is disclosed in U.S. Pat. No. 5,092,510, issued to Anstrom et al. In this instance, a support fixture is positioned under the back side of the PCB and urged upward into temporary contact opposite the mounting location on the top side of the PCB. In one embodiment, a flexible fluid filled bag is utilized in conjunction with the support fixture so that the presence of components on the back side of the circuit board may be accommodated while supporting the circuit board during component mounting. The support fixture may also be selectively rotated to accommodate rectangular components in multiple orientations.
Although the Anstrom technique provides a usable solution for back side support, it requires significant circuit and mechanical complexities in order to constantly position the support fixture opposite the mounting location on the other side. Such complexities, obviously, contribute to undesirable, excessive, manufacturing costs. Furthermore, the support fixture only provides support to a single mounting location on the top side of the PCB. Consequently, either the support fixture or the PCB must constantly be positioned to mirror component placement on the top side.
Given these limitations of the prior art, there is a clear need for an improved PCB support apparatus and method. Accordingly, objects of the present invention are to provide a mechanically simplified, easy-to-use, and cost effective support apparatus and method for component placement and other PCB assembly purposes.